My perspective is from a future work potential point of view. As someone who hasn't been a student for 10 years (MPH grad 2009 from a top 10 PH school) but has been working in international public health all that time, this is what I'll say to you:
1.) As you know, medical school is hard and is kind of an endurance test that requires a lot of commitment and focus on your end goal. I didn't go to medical school, but I know this because I'm friends with people who did/work with people who did. That said, the MD-MPH pathway is excellent if you're interested in working in high level public health interventions on the field. Even if you never see a single patient (manyof the MD-MPHs I work with occasionally volunteer in their organization's service delivery clinic just to keep their licence going), that combo opens doors because yes, you're right- MPHs have become a dime a dozen. To be honest, even without an MPH, if you can demonstrate some commitment and interest as an MD into community health, you're emminently employable in the field. But with this option, you'll have to slog through the years of medical school doing things you might not enjoy and knowing that it's just a means to a slighly better advantaged end and it's not something that is actually necessary.
2.) It is not true that an MD-MPH pathway is more prestigious or advantageous than an MPH or MSPH- PhD pathway. The PhD route is also pretty prestigious and important on the job market. That's why 10 years after graduation, I'm putting myself through the PhD/DrPH application cycle and horrors of the GRE because whatever anyone says, the truth is there's only so far an MPH will take you in this field. I'd say work experience counts a lot (in addition to degrees) if you're going to be interested in health behaviour, health education, community health-focused fields like I am, but your interests seem to lie more in epidemiology and possibly biomedical sciences for public health- type route, and a PhD is emminently important in those areas. Based on what you've said, I think the PhD route may be more enjoyable and personally fulfilling route for you. Because frankly, I know MDs who have ended up going back to get a PhD in public health because their area of interest and focus was so far removed from medical practice.
3.) Nothing is set in stone. Yes, it is good to be strategic in making grad school decisions when you're "young," but just because you go for an MPH or public health science-related masters program now doesn't mean you can't go to med school later on of afterwards. A former classmate of mine just started med school last year after a decade working in public health. It's never too late. One thing I know for sure is that forcing a circle into a square is rarely a good idea. Very little sucks as much as forcing yourself into a box you know doesn't fit what you want. It makes learning and life a drag and steals your happiness. It's not a matter of competence. I would say going to medical school seems to me to be a harder way of achieving your current goals. That said, if you think you might want to practice medicine at any point or be more involved in the clinical areas of research or implementation in public health, then definitely go and do the MD first. Getting an MPH first makes no sense to me in that instance. In fact, to me, if you're strongly feeling that some level of clinical practiced might be in your future, you'd be better off trying to get into some sort of MD/MPH dual degree program or an MD/PhD program in a school that offers the combo with public health areas like epidemiology or data science or health behaviour, health policy etc. If you're not so fussed about interacting with patients, then go ahead and do the public health (MPH, MSPH, Masters program by any name) Masters with an eye on getting the PhD after. Do your PhD AS SOON AFTER the Masters as you possibly can. Don't be like me and think, "oh I'm overqualified and underexperienced, let me go work for a few years." A few years will turn into several and there will always be excuses as to why you'll apply next year. Once you get sucked into work, it's hard to leave but the PhD is a good move for a career in public health. Which is why I'm back after 10 years out of school, applying to doctoral programs. Sigh.
I don't know if this has helped you any. Hopefully, I've shed some light on longer term things you should be considering beyond school. Congrats on your acceptances so far and good luck with your studies whatever you choose to do.